This invention relates to a circuit comprising series-connected semiconductor elements which are each provided with a controlled avalanche region.
It is a well known measure to arrange elements in series which are each capable of withstanding only a limited voltage in order that a higher voltage thus can be admitted across the whole bipole.
A problem arising in such a series arrangement is the voltage distribution between the elements. Solutions for this problem have already been suggested.
FIG. 1 of the Japanese Patent Application No. 118,357 of 1978 shows that more or less equal or admissible voltages are produced across the elements when each element has connected in parallel with it a resistor which provides a current distribution. FIG. 2 indicates that in the case of a rectifier subjected to a high reverse voltage each diode can be irradiated with light in order to produce, besides the (dark) leakage current, a further photocurrent, as a result of which a correct current distribution is also obtained. In the Philips Data Handbook for Semiconductors for the year 1980, Part S2 about Power Diodes, Thyristors, Triacs, there is indicated for the BYX 25 series on page "September 1979, 4" that there is also a third possibility of arranging in series elements or semiconductor elements and so in this case diodes without further steps being taken for obtaining a satisfactory voltage distribution. This possibility arises when the element has a controlled avalanche characteristic. The said devices are therefore of the type having a controlled avalanche characteristic.